Disc drive memory systems have been used in computers for many years for storage of digital information. Information is recorded on concentric memory tracks of a magnetic disc medium, the actual information being stored in the form of magnetic transitions within the medium. The discs themselves are rotatably mounted on a spindle the information being accessed by means of read/write heads generally located on a pivoting arm which moves radially over the surface of the disc. The read/write heads or transducers must be accurately aligned with the storage tracks on the disc to ensure proper reading and writing of information.
During operation, the discs are rotated at very high speeds within an enclosed housing by means of an electric motor generally located inside the hub or below the discs. One type of motor in common use is known as an in-hub or in-spindle motor. Such in-spindle motors typically have a spindle mounted by means of two ball bearing systems to a motor shaft disposed in the center of the hub. However, with the decreasing size of information storage systems, other types of bearings including hydrodynamic bearings are being developed. Useful designs are disclosed in the incorporated applications.
In these types of systems, lubricating fluid--either gas or liquid--functions as the actual bearing surface between a stationary base or housing and the rotating spindle or rotating hub and the stationary surrounding portion of the motor. For example, liquid lubricants comprising oil, more complex ferro-magnetic fluids, or even air have been utilized for use in hydrodynamic bearing systems. The reason for the popularity of the use of air, is the importance of avoiding the outgassing of contaminants into the sealed area of the head disc housing. However, air does not provide the lubricating qualities of oil. Its low viscosity requires smaller bearing gaps and therefore higher tolerance standards to achieve similar dynamic performance.
Thus, in the case of a hydrodynamic bearing employing a liquid lubricant, the lubricating fluid and its components must be sealed within the bearing to avoid loss of lubricant which results in reduced bearing load capacity. Otherwise, the physical surfaces of the spindle and housing could contact one another, leading to increased wear and eventual failure of the bearing system. Equally seriously, loss of a seal or failure to control the fluid level within the bearing system could cause contamination of the hard disk drive with lubricant particles and droplets as well as outgassing-related condensation.
A further difficulty with prior art designs of liquid lubrication hydrodynamic bearings is that frequently voids or gas bubbles may occur in the bearing area.
Temperature changes of the assembly will result in volume changes of (in order of importance) the gas bubbles, the liquid lubricant and the solid container (i.e. bearing assembly internal volume). Generally the volume of gas bubbles and volume will increase relative to its containers. Thus the problem presented is to prevent the lubricant from spilling out of the container if such a relative increase in volume occurs.